ARC4RANDOM(3C) Standard C Library Functions ARC4RANDOM(3C)

## NAME

**arc4random**, **arc4random_buf**, **arc4random_uniform **- random number generator

## SYNOPSIS

**#include <stdlib.h>**

__uint32_t__

**arc4random**(__void__);

__void__

**arc4random_buf**(__void__ __*buf__, __size_t__ __nbytes__);

__uint32_t__

**arc4random_uniform**(__uint32_t__ __upper_bound__);

## DESCRIPTION

This family of functions provides higher quality data than those described

in rand(3C), random(3C), and rand48(3C).

Use of these functions is encouraged for almost all random number

consumption because the other interfaces are deficient in either quality,

portability, standardization, or availability. These functions can be

called in almost all coding environments, including pthreads(5) and

chroot(2).

High quality 32-bit pseudo-random numbers are generated very quickly. On

each call, a cryptographic pseudo-random number generator is used to

generate a new result. One data pool is used for all consumers in a

process, so that consumption under program flow can act as additional

stirring. The subsystem is re-seeded from the kernel random number

subsystem using getentropy(3C) on a regular basis, and also upon fork(2).

The**arc4random**() function returns a single 32-bit value.

**arc4random_buf**() fills the region __buf__ of length __nbytes__ with random data.

**arc4random_uniform**() will return a single 32-bit value, uniformly

distributed but less than__upper_bound__. This is recommended over

constructions like "arc4random() % upper_bound" as it avoids "modulo bias"

when the upper bound is not a power of two. In the worst case, this

function may consume multiple iterations to ensure uniformity; see the

source code to understand the problem and solution.

## RETURN VALUES

These functions are always successful, and no return value is reserved to

indicate an error.

## INTERFACE STABILITY

**Committed**

**MT-LEVEL**

**MT-Safe**

## SEE ALSO

rand(3C), rand48(3C), random(3C)

OmniOS December 31, 2014 OmniOS

This family of functions provides higher quality data than those described

in rand(3C), random(3C), and rand48(3C).

Use of these functions is encouraged for almost all random number

consumption because the other interfaces are deficient in either quality,

portability, standardization, or availability. These functions can be

called in almost all coding environments, including pthreads(5) and

chroot(2).

High quality 32-bit pseudo-random numbers are generated very quickly. On

each call, a cryptographic pseudo-random number generator is used to

generate a new result. One data pool is used for all consumers in a

process, so that consumption under program flow can act as additional

stirring. The subsystem is re-seeded from the kernel random number

subsystem using getentropy(3C) on a regular basis, and also upon fork(2).

The

distributed but less than

constructions like "arc4random() % upper_bound" as it avoids "modulo bias"

when the upper bound is not a power of two. In the worst case, this

function may consume multiple iterations to ensure uniformity; see the

source code to understand the problem and solution.

These functions are always successful, and no return value is reserved to

indicate an error.

rand(3C), rand48(3C), random(3C)

OmniOS December 31, 2014 OmniOS